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Tracking Down Offenders with the DNA of their Relatives

written by: •edited by: Paul Arnold•updated: 5/6/2011

DNA fingerprinting was first used in a criminal investigation in 1986. Since then it's been used to crack thousands of cases all over the world. The technology has also been extended to use the DNA of family members to track down an offender.

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    DNA fingerprinting has now become a forensic science tool that is regularly used in police investigations. The trawl through DNA databases to find a match with the genetic material found at a crime scene has been expanded to include a search for the DNA of close relatives. Sometimes when police have obtained a DNA profile it doesn't correspond to any in the database. There is no exact match. So the search can be expanded to look for DNA that is very similar to the crime scene sample. It's based on the very simple premise that the genetic profile of individuals who are related to each other will contain more similarities than those that aren't.

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    Familial Searching

    In October 1986 a 22 year old woman from Killingworth in the north of England was walking home when she was attacked and raped. Despite an intensive police investigation the attacker remained at large. The case went cold but detectives revisited it nearly 20 years later. To track down the attacker they took advantage of a recent innovation in forensic science, Familial searching, which was developed by the UK's Forensic Science Service.

    A microscope slide containing biological material from the victim was retrieved and a DNA profile was obtained using a technique known as Low Copy Number. Here a DNA profile can be obtained from a tiny sample of genetic material, from as few as 5-10 cells or from a sample where the DNA is in a poor condition. Typically the DNA will be copied 34 times, as opposed to the standard 28 for DNA profiling; it is a much more sensitive test.

    The DNA profile obtained in this cold case was compared with others in the national database. Several were found that were a close enough match to suggest that the profiles were related. Further inquiries led to a 50 year old man, Russell Bradbury, who pleaded guilty and was jailed for six and a half years. Although Bradbury's DNA wasn't on the database, a relative of his was. This wasn't the first time that Familial searching had been used to catch a criminal, but it's one of the most famous and it showed police that the passage of time need not be a barrier to solving a case.

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    The Forensic Science Service,

    BBC News,